1. Field of the Invention
The present invention relates to a heavy metal detecting device and the fabricating method thereof, and more particularly, the present invention relates to a heavy metal detecting device and the fabricating method thereof with on-site quick detecting characteristic.
2. Description of the Prior Art
According to the announcement of EPA of Taiwan, the standard detecting method for detecting the Hg ions in the ground water is known as “the metal in the water and the micro-element detecting method, inductively coupled plasma atomic emission spectroscopy (W311.53C). This method can improve the accuracy of the analysis of the micro-element for detecting the different metal ions in the sample and further reach the limit of detecting the Hg ions up to 2×10−5 mg/L, which is extremely suitable for detecting the heavy metal pollution. However, expensive devices, experienced operators and complicate process are required for this method, so the government needs to spend lots of time and money to monitor the environmental pollution. If the analysis is able to be done quickly on the spot and only the samples with the positive test brought back to the laboratory, the cost will be down because the amount of the samples is greatly decreased. That is to say, it will save money and time for monitoring. Nowadays, the heavy metal pollution is usually on-site detected by X-Ray Fluorescence (XRF). XRF is a device which emits X-ray with high power to light the analyte, and the user conducts the qualitative and quantitative analysis on the intensity of the power of the light. XRF has many advantages like rapidity, convenience and non-destruction. However, XRF has many disadvantages such as expensive (for example, one million Taiwan dollars per device), easy to be affected by the spectrum of the different elements (for example, the spectrum of Pb and Hg is duplicable), easy to be affected by the environmental factors like the temperature and the liquid sample, and insensitive to some elements (for example, the detection limit for Hg ranges from 20 mg/L to 50 mg/L). Therefore, the detecting technique for detecting the Hg pollution has a large room for improvement. Namely, there are a lot of business opportunities.
On the other side, because the nano-metal-particle has specific physical and chemical property, the nano-metal-particle is applied on the chemical detecting devices and photoelectric application. For example, the nano-metal-particle has a specific optical phenomenon—surface plasmon resonance (SPR). The resonance generated by the electromagnetic wave interacting with the electron of the metal when the electromagnetic wave with specific wavelength lights to the nano-metal-particle is called SPR. More importantly, SPR is affected by the composition, shape and size of the particle and the environment surrounding the particle. Besides, the nano-metal particle has high ratio of the surface area and adequate chemical characteristic on its surface, which can be easily changed by modifying the ligand/surfactant molecules being adsorbed on its surface. The function is able to be different by modifying the functional group, which makes it be widely used in a variety of chemical and biological analysis technology. For example, Au nano-particle with positive or negative surface has high dissolving characteristic in the solution, and the Au nano-particle will appear red when the peak of the absorption is 520 nm. When the surface of Au nano-particle reacts with the specific analytes, the particles get together because the surface-charge is neutralized, or there is a connection between two nano-particles. When the particles get together, the distance between the two particles is changed, and then the state of SPR is changed. At this moment, the absorption peak red-shifts between 600 nm to 700 nm, the color of the solution becomes blue. When the concentration of the analyte changes, the color changes as well. The change of the color is able to be observed by eyes or be analyzed by the spectrometer. Thus, the chemical detecting device is invested by utilizing the colorimetric method.
In recent years, Au nano-particle is widely used as the probe of the colorimetric method worldwide. The detecting targets comprise heavy metal ion, glucose, protein and DNA. A lot of people pay high attention on this method. Professor Mirkin and his research team published that the Au nano-particle modified with DNA can be used as colorimetric probe for detecting Hg ions by utilizing the thymine-Hg2+-thymine to form the connection among the Au nano-particles, which made the particles get together and the color changed, and the limit of detecting was reached to 0.01 mg/L. Professor Xiaodong Chen and his research team simplified the complication of the synthesis. They used the uric acid to be the surface decoration of the Au nano-particle and achieved the detecting limit, [Hg2+]=0.01 mg/L. However, even though the Hg detecting method with utilizing Au nano-particles can achieve very low detecting concentration, it is complicate for the laboratories to do the process. The efficiency of the method is low. The solution used in the method is hard to carry, easy to leak and hard to reserve. Moreover, there are a lot of unavoidable human errors. When the detecting process is operated, the change of the color is not obvious. In the recent research, Professor Chien-Fu Chen made Au nano-particles react with Hg ions in the solution first, and dropped it on the filter paper to recognize the color until achieving the detecting concentration, to 0.01 mg/L. In this experiment, Au nano-particles solution is still needed to be the probe even though it has the problems mentioned above (hard to reserve, carry and process). So, there are a lot of rooms needed to be improved if it serves as a rapid detecting platform.